HIGHLY DISPERSED AND A SINGLE-SITE PLATINUM CATALYSTS SUPPORTED ON SILICA-ALUMINA FOR CO OXIDATION AND PROPANE DEHYDROGENATION

Abstract

The characteristics of SiO2-Al2O3 supports were tuned by three strategies in order to achieve highly dispersed, especially single-atom Pt sites using for CO oxidation or propane dehydrogenation (PDH). The strategies include incorporation of χ-Al2O3 and Si into γ-Al2O3 via solvothermal, variation of SiO2 content of Si-doped γ-Al2O3 via dry impregnation, and use of KLTL zeolite as a highly crystalline support. The results showed that dispersity could be effectively enhanced by incorporating dopants (χ-Al2O3 and Si). Pt-support interaction was particularly strengthened on Si-doped Al2O3 at low SiO2 loading, promoting highly dispersed Pt sites. The results from CO oxidation tests revealed a linear relationship between TOFs and amount of surface basicity of modified supports. It is suggested oxygen mobility plays a distinct role in controlling the surface reaction between CO* and O*, which were activated by different adjacent Pt sites. The proposed mechanism was strengthened by the TOFs of the modified catalysts in PDH remained unchanged. In addition, these highly dispersed Pt catalysts can also be applied in PDH due to the promotional effect on activity and selectivity to propylene. Interestingly, when dispersed Pt on KLTL zeolite, the first site-isolated mononuclear Pt catalyst with a well-defined structures and locations is presented. IR and X-ray absorption spectra and electron micrographs determine the structures and locations of the Pt complexes in the zeolite pores, demonstrate the platinum support bonding, and relationship between active site structures and catalytic performance. Furthermore, the single-atom Pt catalysts can be accounted as ideally catalytic sites in structure-insensitive reactions.